Thai police detained more than 200 tourists in a drugs bust at an illegal karaoke bar in Bangkok on Wednesday.
Dazed and confused revelers -- debris party littered around them -- were seen huddled under bright lights at the Sathorn district venue in official police photos and Thai media footage.
The majority of those involved were Chinese nationals, Royal Thai police spokesperson Archayon Kraithong said.
"The police conducted a urine test and found out that they have used illegal substances," he said.
Further tests will be carried out to identify which drugs the tourists had taken, and a decision will then be made on whether to prosecute any of them, Archayon said.
A post on the official Thai police Facebook page said that among the drugs believed to have been found were ketamine, as well as traces of MDMA, methamphetamine, and diazepam.
"The police discovered that the entertainment venue appears to sell drugs to customers," the post said.
It added that "there is also a drug deposit service, with customers able to gamble without fear of the authorities and the law".
Thailand, a major transit hub for narcotics from the so-called "Golden Triangle", has tough anti-drugs laws.
Possession of category one drugs, which include MDMA and methamphetamine, can bring jail sentences of up to 10 years.